Froth flotation of iron ores, including use of alkali phosphate



- 3i 1950 E. c. HERKENHOFF FRoTH FLoTATIoN oF IRoN omas INCLUDING usE 0F ALKALI PHosPHATE Original Filed June 10, 1944 ATTORN EY Patented Jan. 3l, 1950 FBOTH FLOTATION F IRON DRES, INCLUD- ING USE OF ALKALI PHOSPHATE Earl C. Herkenhoi, Longmont, Colo., assignor tol American Cyanamid Company, New York, N. Y., a corporation of Maine @riginal application .lune 10, 1944, Serial No. 539,691, now Patent No. 2,466,987, dated April 12, 1949. Divided and this application October 5, 1948, Serial No. 52,960

d Claims. (C11. 209-166) This invention relates to the beneliciation of iron ores by froth iiotation. More particularly, the invention relates to the use of alkali phosphates in a two-stage flotation process suitable for use on lines such as are found in the overflow from iron ore washer plants; in waste products from heavy media separation processes and on those ores which must be nely ground in order to unlock the iron minerals from the gangue.

The present invention is drawn to a division of my copending application Serial No. 539,691, led June 10, 1944, patented April 12, 1949, No. 2,466,987, which was copending with and a continuation-impart of Serial No. 468,524, led Dccember 10, 19112, now Patent 2,389,727, granted November 27, 1945, on a multi-stage flotation process.

One of the principal objectionable constituents in much of the naturally-occurring iron ore is usually a silica-bearing mineral of some type or other. From the point of view of susceptibility to froth notation, this is particularly unfortunate since the iron minerals and these silica-bearing gangues are generally ,difficult to separate. Because of this separational dimculty, a flotation process to be successfully carried out requires careful handling,` usually also accompanied by a high reagent consumption. All of these factorstend to increase the cost of processing. Yet iron ores, despite the fact that they must be handled in enormous quantities, are intrinsically cheap products and the margin of profit is small. Therefore benelciation by froth flotation; if it is to he carrled out, must be done cheaply, easily and efiiciently. in this respect, ordinary methods of beneiiciating ores by froth notation when applied to iron ores leave much to be desired.

Ordinarily, separation of mineral Values from silica-bearing gangues by froth notation takes one of two forms. Either the mineral values are oated from the silica by the use of an anionictype reagent or reagent combination, or the silica is heated from the mineral values by means of a cationic-type of reagent. In general, anionic dotation is the easiest and cheapest and is, therefore, used whenever possible. The usual procedures are old and well known in conjunction with many ores. l

Usually, when applied to ordinary iron ores oi the type with which the present invention is concerned, a straight anionic iiotation does not work well. The iron. .minerals and the gangue tend to tloat together. By using sufficient care and the necessary large amount of reagents a beneciation be carried out whereby some 30 to 40% ofthe iron values can be recovered, but the grade of concentrate is usually too low. The grade can be improved somewhat at the expense of the recovery, but the net cost is much higher than is practically desirable for the amount of mineral recovered at the corresponding concentrations.

In such cases with other ores, the reverse procedure has been found useful, i. e., silica is floated from the mineral values with a cationic-type promoter. This process, when it can be properly used. gives good results. However, it suffers from several inherent drawbacks which must be overcome. First of all, the reagents are relatively expensive, the unit cost being several times that of equal amounts of anionic-type reagents. They depend for competitive success on the fact that if they can be used effectively they are highly selective, having great collecting power for silica and so can be used in smaller amounts.

Moreover, they must be very emciently used and this involves a second dimculty, that of slimes. Cationic reagents are particularly sensitive to the presence of slimes, even a fraction of a percent in the pulp being sufficient to impair the efciency of the reagent to a point where the reagent cost becomes prohibitive. Still another difiiculty arises from the fact that cationic reagents are considerably less effective on coarse silica than on fine. If silica particles are present in a wide size range and a cationic reagent is used in sufficient quantities to float the coarsest silica particles its selectivity is greatly impaired.

In practical cationic operation, a balance must `be made between the cost of preparing the ore such as the grinding, deslixning, etc., the reagent cost, and the Value oi' the minerals recovered. Unfortunately, in attempting to iioat silica from most low-grade iron ores this balance can not be satisfactorily accomplished. 'Ihe cost. of pretreating the ore to the optimum extent plus the reagent cost ordinarily raises the total above that which can'he expended for the amount of ore recovered if the latter is to be sold in a competitive market.

There remains, therefore, a demand for a suitable beneficiation process whereby the iron content of low grade ores, particularly the wastes from washer plants and the like, can be carried out at a cost which will permit the process to be used on a large scale. It is the object of the present invention to establish a procedure of froth flotation by the use of which the desirable results of cheaper and more effective concentration of the iron minerals may be obtained with these low-grade starting materials.

In general, the desired object of the present invention is accomplished by a two-stage flotation. In the first stage, a major portion of the iron minerals together with a part of the gangue is floated away from the remainder of the ore by means of an anionic-type promoter. This concentrate is then treated with a suitable surface-modifying agent adapted to overcome the effect of the anionic reagent without destroying the potential floatability of the silica. The conditioned ore is then subjected to flotation with a cationic-type reagent and the tailing from this operation constitutes the finished product, or iron concentrates.

The procedure has a number of advantages. Lower cost reagents are used on the biggest bulk of material, whereby the latter is very appreciably reduced before the more expensive reagents need be employed. In this way the better features of both types of reagent are utilized to fullest advantage. A greater proportion of the iron minerals can be recovered in a good grade product than is practically possible by conventional single-stage operation. The present process produces an even greater saving than that of my previously identified copending application in that it eliminates the primary silica flotation. The present process, therefore, is not only highly efficient as compared with older methods, but is also less expensive and readily adapted to use on a large scale.

The process of the present invention will be more fully illustrated in conjunction with the accompanying drawing. The latter sets forth a flow scheme incorporating the principal steps whereby the important advantages of the present invention are obtained.

The ore, as it is introduced into the process of the present invention is assumed to have been previously reduced to a suitable particle size. It may be deslimed if necessary. The desliming step, however, is optional. as shown in the drawing, and the ore may be directly conditioned with the anionic-type promoter. If a frother is desirable with the particular anionic collector, it is ordinarily added at the same time.

After being conditioned the pulp is subjected to the first flotation step, whereby a concentrate rich in iron but containing a part of the gangue, is obtained. The tailing is normally discarded as shown in the flow sheet. With some ores, this fraction may have a rather high iron assay, due to the presence of coarse, or middlimr particles of iron minerals. However, even in such cases, it represents only a small fraction of the total iron in the feed and may be discarded without further treatment. Ifl so desired, the rougher concentrate produced in the anionic flotation may be given an optional cleaning, the tailing from which may be either discarded or recycled to the original conditioning step.

At this point. the rougher, or optionally the cleaner concentrate, is subjected to a step of primary importance in the present process. In this operation it is conditioned with a depressant and/or dispersant. This treatment not only serves the several purposes of overcoming the effects of any residual anionic reagent from the rst notation and dispersing the iron minerals but is of definite assistance in the subsequent flotation of silica.

After being conditioned, the pulp is subjected toy may be either discarded or given an optional cleaning. In the latter case the cleaner concentrate is discarded and the cleaner tailing recycled to the dispersant conditioning step.

Since a principal purpose of the dispersant conditioning operation is to modify the flotation characteristics of the minerals, but the presence of excess dispersant and depressants is objectionable during cationic flotation, the conditioned ore is ordinarily deslimed and washed before adding the cationic reagent. As shown in the drawing, however, when such an excess is not present and the conditioning operation has not created suincient slimes to interfere with the cationic reagent, this step may be by-passed. In fact, small amounts of certain reagents when present during the cationic flotation have a beneficial, selective depressant effect on the iron minerals.

It is an advantage of the present process that despite its being a two-stage flotation operation, it is in fact quite flexible and is readily adjusted for different ores. This may be noted, for example, in the several optional desliming and/or cleaning steps. In this regard, the cleaning is preferably done by flotation, but it is also possible to use gravity methods of concentration such as tabling or vanning when such methods are advantageous.

It is also an advantage that the reagents used may be varied considerably without departing from the scope of the present invention. For example, in the anionic flotation a wide range of suitable promoters is available. Excellent results can be obtained for example using an anionic promoter of the higher aliphatic fatty-acid type. Typically good results are obtained using a fatty-acid promotor such as oleic acid. Other reagents which may be substituted therefor include, for example, the lsh oil fatty-acids, cocoanut oil fatty-acids, linseed oil fatty-acids, cottonseed oil fatty-acids, resin acids, naphthenic acids. talloel and the like, sulfonates of these and like acids and sodium, potassium and ammonium soaps and emulsions thereof.

Excellent results are also obtained using as the anionic promoter, a reagent of the sulfonated hydrocarbon type. As in using fatty-acid reagents, the choice of a particular sulfonatedhydrocarbon reagent may be from a wide range of materials. By way of example, both the oil-soluble, water-disperslble reagents of the mahogany acid or mahogany soap types, and the water-soluble green acid or green soap types. Such sulfonated products are commercially available in a number of different forms. However, as shown, for example, in U. S. Patent 2,331,049, their principal source is as by-products from the refining of petroleum lubricating oil fractions in the course of treatment with fuming sulfuric acids or sulfuric acids. When so produced, these by-products are generally found to be salts of the sulfonated hydrocarbons, most commonly the sodium salt although other salts may be encountered. In some cases no attempt has been made to neutralize the acid product. Even after neutralization, free sulfonates and/or sulfates are often found.

In many cases, it is desirable to use a frother in conjunction with the anionic-type promoter. Any of the well-known frothers may be used. Among these are included, for example, pine oil, synthetic pine oil, cresylic acids, and the commercially available, aliphatic alcoholic frothers.

si 'These may be used alone, in admixture with each other, or with other froth modifying agents. In general, the fatty-acid type reagents require more careful use of frothing agents whereas the sulfonated-hydrocarbon types often require little frother or none at all.

In my three-stage process, lime, or an equivalent alkaline earth hydroxide, was used alone, in amounts up to about 5.0 lbs/ton of original ore, as the iron mineral depressant. This was found to leave the'anionic concentrate in such a condition that the silica tended to float in the presence of a frother, although carrying with it a considerable proportion of iron. In my previous process this was turned to advantage to conduct a primary silica flotation without additional reagents, other than the possible use of a frother. Lime, or its equivalent, did not cornpletely overcome the eect of the anionic reagents on the mineral surfaces.

According to the present process, it has been found that if the lime, or some other alkaline material such as soda ash or another alkaline-earthhydroxide is suitably supplemented, this primary silica flotation is unnecessary. Such supple- Surface-modifying agents found suitable for 1 this purpose include for example, tannie acid, Quebracho, dextrin (particularly yellow corn dextrin) and a number of phosphates such as tri-sodium phosphate, tetra-sodium pyrophosphate, sodium acid pyrophosphate and the like. For the purposes of the present invention, these are all considered to be effective as dispersing agents, although their action also is probably depressant to a certain extent.

When sulfonated-hydrocarbon types of reagents are used in the initial or anionic flotation operation, quebracho is particularly effective, even with greatly4 reduced amounts of lime as compared to those required when using fatty-acid type reagents. In some instances, the use of lime even may be unnecessary and effective depression of the iron minerals maybe accomplished by the use of the supplementary reagent alone. It should be noted, that anionic reagents of the sulfonated-hydrocarbon type have been found to produce much better results when they are conditioned with flotation feed to which acid has been added.

Similarly, the silica concentration by notation in the presence of a cationic promoter is not necessarily limited to the use of any particular Example 1 As illustrative of the practice and results obtained by straight amonio flotation a sample of overflow waste principally composed of hematite and quartz from an iron ore washer plant, which presented beneciation problems typical of those with which the present invention is concerned, was made into a pulp containing about 20% solids, conditioned with 0.162 lb. per ton of a pine oil frother and 0.75 lb. per ton of oleic acid and subjected to froth flotation for 5 minutes in a. Fagergren flotation machine. The concentrate therefrom was cleaned three times. The cleaned concentrate assayed 26.71% iron and contained 41.66% of the total iron contained in the feed. Since the feed contained 23.24% iron, the degree of concentration achieved is not appreciable. The standard method of anionc-type flotation, therefore, is not practical with this type of ore.

Example 2 The procedure of Example 1 was repeated on the same ore with the exception that the ore was deslimed by hydraulic classification before being subjected to the original conditioning step. From a head assaying 23.84% iron, a concentrate assaying 27.95% iron and containing 37.70% of the reagent. For example, choice as to the cationic y total iron fed was obtained. The results, while better than those of Example 1 are obviously not satisfactory from a commercial point of view.

Eample 3 In order to obtain a basis for comparison, another similar sample was given the following treatment. A pulp of the ore (60% solids) was ground for 12 minutes with 20 lbs. per ton of sodium silicate and the ground ore deslimed by hydraulic classification. The deslimed ore was diluted to 20% solids, conditioned with 0.054 lb. per ton of pine oil, 1.0 lb. per ton of lime and 0.15 lb. per ton of octadecylamine and finally oated for three minutes. Promotion was unsatisfactory and the amount of cationic agent was increased. Finally using several times the original amount a concentrate representing 18% of the ore, containing 35% of the original iron and assaying 56.32% Fe was obtained. While the grade was satisfactory, the recovery is not and the reagent consumption was too high for industrial use.

The preceding examples show that when either anionic or cationic reagents are used alone in a single-stage flotation operation, the results produced are not particularly useful. 'Ihe concentrates obtained are either too poor in grade or contain too small a fraction of the original iron or the reagent consumption is too high to be practical. By way of comparison anumber of samples of different ores were then treated according to the process of the present invention using a variety of reagent combinations.

Example 4 A sample of a low-grade Minnesota iron ore was ground to about minus 20 mesh, deslimed hydraulically, conditioned for' 2 minutes with 1.96 lbs. per ton of oleic acid and floated for two minutes. The concentrate was then conditioned for 2 minutes with 2.0 lbs. per ton of lime and 0.5 lb. per ton of sodium acid pyrophosphate, deslimed and Washed. The slimes removed'were designated fines A 5 minute notation was then carried out using 0.11 lb. per ton of pine oil and 0.25 lb. per ton of lauryl amine hydrochloride. Excellent grade and fair recovery were obtained as shown in table.

Table Percent Assay Per- Distribution Product Weight cent Fe Percent Fe With some ores it may be desirable to improve y recovery by reducing iron loss. A minor part of Athis loss is unavoidable because of the iron minerals carried away in the desliming operation. However, the principal diil'iculty is that the anionc-ilotation recovery (rougher concentrate) is too low. This may be improved when using sulfonated reagents by conditioning .the ore with acid before the anionic notation, in accordance with the disclosure of my joint application with R. B. Booth, Serial No. 481,906, led April 5, 19,43, now U. S. Patent No. 2,410,376. Enough alkaline material is used to produce an alkaline pH as well as to induce the desired surface conditions.

When an acid-treated ore is treated with a sulfonated reagent, the alkaline material may be one of the same alkaline conditioning agents previously noted. However, for the Purposes of overcoming the eilect of the acid any strong alkali such as caustic soda, potash and the like y may be used. Similarly, excess acid may be remoter. selected from the group consisting of the higher aliphatic fatty acids, resin acids, naphthenic acids, talloel, sulfonates of such acids, sodium, potassium and ammonium soaps emulsions thereof and sulfonated petroleum hydrocarbons of the oil-soluble water-dispersible mahogany acid and mahogany soap types and the water-soluble green acid and green soap types obtained in the acid treating in refining lubricating oils; collecting the resultant iron-minerals-rich froth concentrate; conditioning an aqueous pulp of the iron concentrate with (a) a material. selected from the group consisting of the alkali and alkaline-earth metal hydroxides and carbonates, in amount sumcient to overcome' the im, dency of vthe iron minerais as activated by vuns' anionic promoter to iloat and to maintain an alkaline pH; and (b) a water-soluble alkali phosphate as a surface-modifying agent, in sumcient amount to prevent flotation of oxidized-iron minerals in the presence of a cationic-type promoter for acidic gangue; subjecting the conditioned concentrate to froth notation in the presence of a cationic-type promoter, selected from the group consisting of the long-chain aliphatic amines containing 12-18 'carbon atoms. quaternary onium" compounds, and the polyalkylene-polyamine-reaction-products type. used in amount suiiicient to remove the excess acidic gangue and collecting the tailing which is rich in iron and low in gangue.

2. A process according to claim 1 characterised in that the surface-modifying agent is tri-sodium phosphate.

3. A process according to claim 1 characterised in that the surface-modifying agent is tetrasodium pyrophosphate.

4. A process according to claim 1 characterized in that thesurface-modifying agent is sodium acid pyrophosphate. i

EARL -C. HERKENHOFP.

nml-:NCES man The following Areferences are of record in the /nnqth' y.- oct. 29 im 

1. A PROCESS OF BENEFICIATING OXIDIZED-IRON ORES CONTAINING EXCESSIVE AMOUNTS OF ACIDIC GANGUE WHICH COMPRISES THE STEPS OF FORMING AN AQUOUS PULP OF THE ORE OF A SIZE SUITABLE FOR USE AS FLOTATION FEED; SUBJECTING SAID PULP TO FROTH FLOTATION IN THE PRESENCE OF AN ANIONIC-TYPE PROMOTER, SELECTED FROM THE GROUP CONSISTING OF THE HIGHER ALIPHATIC FATTY ACIDS, RESIN ACIDS, NAPHTHENIC ACIDS, TALLOEL, SULFONATES OF SUCH ACIDS, SODIUM, POTASSIUM AND AMMONIUM SOAPS AND EMULSIONS THEREOF AND SULFONATED PETROLEUM HYDROCARBONS OF THE OIL-SOLUBLE WATER-DISPERSIBLE MAHOGANY ACID AND MAHOGANY SOAP TYPES AND THE WATER-SOLUBLE GREEN ACID AND GREEN SOAP TYPES OBTAINED IN THE ACID IN REFINING LUBRICATING OILS; COLLECTING THE RESULTANT IRON-MINERALS-RICH FROTH CONCENTRATE; CONDITIONING AN AQUEOUS PULP OF THE IRON CONCENTRATE WITH (A) A MATERIAL, SELECTED FROM THE GROUP CONSISTING OF THE ALKALI AND ALKALINE-EARTH METAL HYDROZIDES AND CARBONATES, IN AMOUNT SUFFICIENT TO OVERCOME THE TENDENCY OF THE IRON MINERALS AS ACTIVATED BY THE ANIONIC PROMOTER TO FLOAT AND TO MAINTAIN AN ALKALINE PH; AND (B) A WATER-SOLUBLE ALKALI PHOSPHATE AS A SURFACE-MODIFYING AGENT, IN SUFFICIENT 